The invention pertains to rotary indexing tables such as employed in the machining and fabrication arts.
Rotary index tables are commonly employed with machine tools, such as milling machines and turret lathes, assembly apparatus, bottle filling machines, and the like, wherein the table is periodically indexed about its axis of rotation for sequentially presenting a station or part to a tool, or nozzle, or other similar fixture. The rotation of the index table may be manually accomplished, or power driven such as by a rotary or reciprocating motor which may be electric or fluid powered. The most conventional system for indexing an index table is to utilize a ratchet wheel having teeth defined thereon which are selectively engaged by a ratchet dog, usually pivotally mounted and often spring biased, which engages with the wheel as the dog oscillates about the table axis of rotation in the indexing direction. As the dog is oscillated in the return direction it rides over the teeth of the ratchet wheel, and adjustable means are often associated with the ratchet dog linkage to limit the angular degree of dog movement about the table axis in order to vary the extent of table rotation.
Indexing devices utilizing pivoted ratchet dogs produce a positive engagement between the table ratchet wheel and dog in only the direction of rotation when the dog is rotating the wheel. Indexing tables must be indexed precisely to predetermined positions. Thus, it is necessary for the ratchet dog to move the index table to the predetermined rotational location, and no further. However, with most of the high speed machine tools and apparatus presently being utilized it is necessary to rotate the index table rapidly, and accurate location of the index table at its termination of rotation in the indexing direction becomes difficult due to the inertia of the table while rotating.
The inertia of the index table tends to continue table rotation after the positive driving of the table by the ratchet dog has ceased. Such " carry-over" of the index table and ratchet wheel past the desired table location is possible because the engagement of the ratchet dog with the ratchet wheel is unidirectional, and the dog cannot prevent rotation of the table ratchet wheel past the desired location as the ratchet dog merely "rides over" the ratchet wheel teeth.
In order that the index wheel and table be accurately located, a radially displaceable index pin or lock is often utilized to position and hold the index table intermediate indexing cycles. It is possible to sequence the operation of a power driven index lock such as to "catch" the index table at the end of its indexing movement to accurately locate the table. However, such an abrupt termination of the table movement as produced by an abutting relationship between table structure and a locating detent imposes undesirable and sudden shocks and impacts upon the index table and locating detent, creating high wear with the likelihood of fracturing the detent, or "peening" the table structure engaged by the locating detent.
While the locating detents of the prior art are capable of accurately predetermining and maintaining the rotational position of the index table relative to its axis of rotation, such locating detents do not usually provide such a degree of interconnection between the index table and its base as to prevent vibration between the table and base, and locking means are often utilized with the table for positively locking the table with respect to its base during functioning of the apparatus mounted upon the table. For instance, if the index table supports a workpiece machined by a milling machine, it is most desirable to firmly lock the index table to its base during such machining in order to prevent inaccuracies developing in the workpiece due to slight movement and vibrations existing between the table and base.
Previously utilized index table locks are often manual, requiring separate attention and operation as compared with the index table operating controls. While expansible motors have been utilized to lock index tables to their base, prior art holding means do not produce symmetric hold-down forces upon the index table, and are expensive and incapable of producing optimum holding forces in a minimum space and configuration.